Use blue-green deployment with Flagger for Supply Chain Choreographer

This topic tells you how to use blue-green deployment with Packages and PackageInstalls using Flagger for Supply Chain Choreographer.

Overview

Blue-green deployment is an application delivery model that lets you gradually transfer user traffic from one version of your app to a later version while both are running in production.

This currently works with only workloads of type server.

Prerequisites

To use blue-green deployment, you must complete the following prerequisites:

• Complete the prerequisites in Configure and deploy to multiple environments with custom parameters.
• Configure Carvel for your supply chain. See Carvel Package Supply Chains.
• Configure a GitOps tool to deploy the package. See Deploy Package and PackageInstall using Flux CD Kustomization or ArgoCD.

Deployment name

To get the name of the deployment you want to use, identify the name of the deployment and service that are part of the PackageInstall by running:

kubectl get deployment --namespace=prod

This displays a list of all the deployments and services in the current Kubernetes namespace, with their current names. For example:

NAME                         READY   UP-TO-DATE   AVAILABLE   AGE
hello-app-deployment         1/1     1            1           103

Flagger Canary resource

Create a canary custom resource using the Flagger instructions using the deployment name from the earlier step.

Flagger creates three ClusterIP services: hello-app.dev.tap-primary, hello-app.dev.tap-canary, hello-app.dev.tap. It also creates a shadow deployment named app-primary that represents the blue version.

When a new version is detected, Flagger scales up the green version and runs the conformance tests, the tests target the hello-app.dev.tap-canary ClusterIP service to reach the green version. If the conformance tests are passing, Flagger starts the load tests and validates them with custom Prometheus queries.

If the load test analysis is successful, Flagger promotes the new version to hello-app.dev.tap-primary and scales down the green version. Flagger extends a canary analysis through custom metrics and webhooks for running load tests, acceptance tests, or any other custom validation.

Flagger includes a load generation tool to ensure that the canary version of an application has enough traffic to generate metrics for analysis.

Without an HPA (Horizontal Pod Autoscaler), Flagger does not dynamically scale up or down the new version based on traffic weight. This implies that the number of pods for the new version remains constant throughout deployment.

Consequently, performance issues like high latency, errors, or timeouts can arise if the new version receives more traffic than it can handle. This situation can also impact the metrics and webhooks that Flagger uses to validate the new version, potentially leading to a rollback or promotion delay.